1. Technical Field
This invention relates to active matrix display controllers. An active matrix display controller is typically an application specific integrated circuit (ASIC) and is one of the support chips accompanying an active matrix flat panel display. The controller takes display data from the host system and provides it, along with control and timing signals, to the column and row drivers of the display panel.
2. Description of Related Art
With recent progress in various aspects of active matrix display technology, the proliferation of active matrix displays has been spectacular in the past several years. In an active matrix display, there is one transistor or switch corresponding to each display cell. An active matrix display is operated by first applying select voltages to a row electrode to activate the gates of that row of cells, and second applying appropriate analog data voltages to the column electrodes to charge each cell in the selected row to a desired voltage level.
To date the controller chips (integrated circuits) used in active matrix displays have been purely digital. However, controlling an active matrix display also requires analog circuitry. Specifically, the column drivers on the periphery of the display panel which supply the analog data voltages to the column electrodes typically need analog reference levels to do digital-to-analog conversion, and these analog reference levels may need to be changed to invert the polarity across the liquid crystal of the display. Because of the large size, power consumption, and heat generation of the analog circuitry, the analog circuitry is not incorporated in the purely digital controller chips of the prior art and must be handled with external circuitry. The presence of external circuitry increases the complexity of manufacturing and assembling the active matrix display system.
In addition, the controller chips to date are very specific to a particular system. The controller chips are typically designed for an active matrix display of a certain resolution and for peripheral drivers of certain manufacturers. The specificity of the design of the controller chips leads to problems and inefficiencies. For example, if a flat panel display manufacturer decides to switch to a different type of column driver, the controller ASIC (application specific integrated circuit) must usually be redesigned.
Furthermore, controller chips to date are rather limited in their ability to dynamically modify operating characteristics of a display. One such characteristic is the display gamma. The display gamma is the functional relationship defined by the amount of light emitted by the display cell, or pixel, as a function of the voltage used to produce it. In an active matrix display this voltage is the analog output of the column drivers. The gamma formula is Light.sub.-- out=voltage.sup.gamma. Typically display software assumes a linear gamma, that is the amount of light emitted is proportional to the voltage. However both CRTs and active matrix displays have inherent non-linearity in the light response to the voltage. In an active matrix display, the non-linear gamma is corrected by the analog reference levels sent to the column drivers.
If the ability to modify the display gamma exists, it is typically implemented with a color look-up table (CLUT) method which is rigid and inefficient. In a system using a CLUT, the digital value that will define the desired analog voltage, is actually used as an index to the CLUT. At each indexed location in the CLUT there is stored a new digital value. It is this value that, when converted to an analog voltage, gives the desired display gamma. Using color look-up tables to achieve non-linear display gammas results in a large number of digital values that correspond to the same transmission value. This is a large price to pay in flat panel displays where the digital values are typically limited to 6 bits (i.e. 64 levels). A more flexible and efficient method for modifying the display gamma is needed so that dynamic adjustments may be made in order to suit the display requirements of particular applications or to compensate for temperature changes which alter the transmission behavior of the display panel.
For the foregoing reasons, there is a need for a flat panel display controller that combines digital and analog circuitry to reduce the complexity of manufacturing and assembling the display system, that is flexible enough to apply to different systems without being redesigned, and that can dynamically modify operating characteristics of the display to suit particular applications and compensate for temperature changes which alter display panel transmission behavior.